The Quebec French interrogative particle <i>tu</i> is phonologically identical to the second person singular subject clitic (disregarding stress) and shows a distribution similar to that of clitic doubling, which is optional in this dialect. More specifically, it is subject to a definiteness effect, previously unnoticed in the literature, in that only definite subjects are acceptable in questions with <i>tu</i>. In this paper I argue that the distribution of the question particle <i>tu</i> and that of clitic doubling are both due to the presence of one feature, namely a Definiteness feature.